The present invention relates to a method of reducing the pulegone and menthofuran contents in mint oils, particularly peppermint oil. In addition, the present invention relates to a method of adding purified mint oil flavors to oral compositions, including chewing gum.
Mint oil flavors utilized in oral compositions naturally vary in their contents of pulegone and menthofuran. Recently, it has been recognized that pulegone is an undesirable component of mint oil flavors because it is a potential toxin. Menthofuran also is undesirable at moderate to high levels in mint oil flavors, because it can contribute dirty or diesel notes to the flavor, and it can readily oxidize to other undesirable compounds.
Pulegone is also known as 5-methyl-2-(1-methylethylidene)cyclo-hexanone, R-(+)-p-menth-4(8)-en-3-one and alternately as 1-methyl-4-isopropylidene-3-cyclohexanone. It has a molecular weight of 152.23 and the chemical structure shown below: ##STR1##
Pulegone is normally present as a liquid and is practically insoluble in water but is miscible in alcohol, ether and chloroform. The levels of pulegone are generally higher in less expensive peppermint oils, such as those obtained from Mentha peperita grown in the Yakima valley of Washington. Pulegone is also present in spearmint oil which is obtained from Mentha spicata and in corn mint oil which is obtained from Mentha arvensis.
Menthofuran is present in peppermint oil and is chemically known as 3,6-dimethyl-4,5,6,7-tetrahydrocoumarone. It has a molecular weight of 150.21 and has the chemical structure shown below: ##STR2##
U.S. Pat. No. 4,861,616 to Spencer, issued Aug. 29, 1989, teaches a method of reducing the pulegone content of peppermint oil which stereospecifically hydrogenates pulegone and increases the menthone and menthol content of peppermint oil. Spencer also discloses enhanced stability against menthofuran oxidative breakdown.
U.S. Pat. No. 4,440,790 to Blackwell et al., issued Apr. 3, 1984, discloses a process of stabilizing peppermint oil, which relates to selectively forming a menthofuran-maleic anhydride adduct. No effect on pulegone content is mentioned, nor does there appear to be a change in the pulegone peaks in FIGS. 1 and 2 (before and after processing, respectively) of Blackwell et al.
What is needed is a method of conveniently removing both pulegone and menthofuran from mint oils without harming the flavor.